I have imposed a new requirement today limiting who can start and receive private conversations. This is in an effort to thwart scammers who have a zero post count but private message others offering to sell their licenses. The restriction is not strict, a user must post at least one (1) post in the forum before being allowed to start and/or receive private conversations.
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Warning: It is recommended that this version of vBulletin should not be deployed on Production Servers at this time. Do so at your own risk.

New Feature: Custom Image Resizing
When images are uploaded to the server, vBulletin will resize them to predetermined sizes set under Settings -> Options -> Message Attachment Options. While there are five different sizes (icon, thumbnail, small, medium, and large), this may not fit all content. In 5.2.4, the editor has been updated to allow custom resizing of images. When you're editing content with an embedded image, you will notice a handle that allows resizing the image in the lower right corner after selecting it. You can resize the image to fit your needs and vBulletin will use the closest image size to keep bandwidth low. Fine-tuning of the image display will be handled by the CSS assigned to the image. The values for this change are stored as JSON within the BBCode for the image itself. The end user should not have to modify this JSON at any time.

New Feature: Avatars shown in @mentions
A new option has been added to show the user's avatar before their name when an @mention or [user] bbcode is placed in the content. This option is enabled by default. If desired, you can disable this at Settings -> Options -> BB Code Settings.

Display Avatars Next to @User Mentions
If set to "Yes", user avatars will be displayed next to @user mentions or instances of the [USER] bbcode in posts.

vBulletin Messenger
Response to this feature has been overwhelmingly positive. We've added enhancements to the functionality. The Messages menu in the header of every page will allow you to start a new message. In addition, we have created two new options to handle the flow of replies to Messenger chats. You can find these under Settings -> Options -> Private Messaging Options.

The first option will allow you to change the flood check value for creating private messages, which Messenger is based on. When upgrading, this will be set to the current Flood Check value (default: 30 seconds) You can lower or increase this to fit your needs. The second option allows you to exempt private message replies from the flood check. This will allow smoother chatting amongst multiple recipients.

Minimum Time Between Private Messages
You may prevent your users from flooding your private message center by activating this feature. By enabling floodcheck, you disallow users from making another private message within a given time span of their last message. In other words, if you set a floodcheck time span of 30 seconds, a user may not create a private message topic or reply within 30 seconds of making his last message. Administrators and moderators are exempt from floodcheck. Recommended: 30 seconds. Type the number of seconds only. Enter 0 to disable this function.

Skip floodcheck for PM Replies
If enabled, the floodcheck is only applied to creating new private message threads. Replying to existing private message topics will be exempt from the floodcheck. This improves the user experience of vB Messenger as users will be able to create replies to each other very quickly in an existing private message thread.

Responsive Improvements
New dropdown menu components are now used throughout the system to bring consistency and increase usability in responsive modes. In addition to this some buttons were not applying the proper CSS. These have been updated.

Finally, when viewing an article section, the layout of articles should adapt to the screen size better. One devices with small screens, they will show as one column regardless of the display columns setting. This improves the usability of the article channels in vBulletin 5.

PHP 5.4.X Support
As announced with the release of 5.2.3, PHP 5.4.0 support is now deprecated.

Database Cleanup
If you upgraded from an older version of vBulletin, there are a number of tables that are considered deprecated and are no longer used in vBulletin 5 Connect. These tables may contain a considerable amount of data and increase the size of your database storage. In order to streamline the database, we are working to remove these unused tables. The tables removed in this version are:

forum

forumread

groupmessage

groupmessage_hash

groupread

navigation

plugin

route

socialgroup

socialgroupcategory

socialgroupicon

socialgroupmember

subscribeforum

subscribethread

subscribegroup

Once these tables are deleted, the information will be gone forever. We suggest that you make a backup of them if you feel you might need the data in the future for some other application.

Warning: It is recommended that this version of vBulletin should not be deployed on Production Servers at this time. Do so at your own risk.